The present invention relates to watch cases whose apparent parts are made of a hard material so as to avoid the risk of being scratched when worn on a wrist.
A first such watch case has been marketed with constant success since 1959. This first watch case is in particular described in Swiss patent specification No. 517963. The constant success of this kind of watch case is due in part to the particular shape of the cap that is shown in FIGS. 1 to 4 of the above specification and which protects the watch in a particularly effective manner.
However, the manufacture of these caps and the manner in which they are secured to an underlying middle have always ran into technical difficulties and many different constructions have been proposed for overcoming these difficulties.
The cap described in Swiss patent specification No. 517963 has an outer, possibly frusto-conical face and on the inside two stepped annular shoulders between which are cylindrical connecting surfaces. It is force-fitted over a correspondingly shaped portion of an underlying middle and glued.
According to Swiss patent specification No. 508925, filed in 1969, the cap is removably mounted by means of an elastic annulus over an underlying middle. To this end, it is formed with an inner groove.
Japanese utility model No. 1046157, filed in 1969, suggests fixing two separate constituent parts of a case body with a malleable metallic element of annular shape sandwiched between the two parts.
Swiss patent specification No. 568040, filed in 1971, proposes still another arrangement by providing a cap having a planar underside in which are embedded tapped studs. The latter enable the cap to be secured to a shoulder on an underlying middle with screws.
Actually, only the arrangement disclosed in the first of the above-mentioned documents has been in constant use, despite the fact that it has always been difficult to achieve an even manufacturing standard.
Recently, however, applicants have found that by giving such a cap a new shape, its manufacture and assembly on an underlying middle could be simplified to a large extent. Further a substantial reduction in the cap's internal stresses had the effect of reducing the likelihood of cracks occurring both during sintering and while wearing the watch.